1/*
2 * Copyright (C) 2013 Apple Inc. All rights reserved.
3 *
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions
6 * are met:
7 * 1. Redistributions of source code must retain the above copyright
8 * notice, this list of conditions and the following disclaimer.
9 * 2. Redistributions in binary form must reproduce the above copyright
10 * notice, this list of conditions and the following disclaimer in the
11 * documentation and/or other materials provided with the distribution.
12 *
13 * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
14 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
15 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
16 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR
17 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
18 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
19 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
20 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
21 * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
22 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
23 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
24 */
25
26#ifndef GCIncomingRefCounted_h
27#define GCIncomingRefCounted_h
28
29#include <wtf/DeferrableRefCounted.h>
30#include <wtf/Vector.h>
31
32namespace JSC {
33
34class JSCell;
35
36// A C-heap-allocated object that may have additional reference counts
37// due to incoming references from the heap, which are tracked in
38// reverse: the object knows its incoming references. Such objects also
39// have the invariant that they don't have references back into the GC
40// heap.
41
42template<typename T>
43class GCIncomingRefCounted : public DeferrableRefCounted<T> {
44public:
45 GCIncomingRefCounted()
46 : m_encodedPointer(0)
47 {
48 }
49
50 ~GCIncomingRefCounted()
51 {
52 if (hasVectorOfCells())
53 delete vectorOfCells();
54 }
55
56 size_t numberOfIncomingReferences() const
57 {
58 if (!hasAnyIncoming())
59 return 0;
60 if (hasSingleton())
61 return 1;
62 return vectorOfCells()->size();
63 }
64
65 JSCell* incomingReferenceAt(size_t index) const
66 {
67 ASSERT(hasAnyIncoming());
68 if (hasSingleton()) {
69 ASSERT(!index);
70 return singleton();
71 }
72 return vectorOfCells()->at(index);
73 }
74
75 // It's generally not a good idea to call this directly, since if this
76 // returns true, you're supposed to add this object to the GC's list.
77 // Call GCIncomingRefCountedSet::addReference() instead.
78 bool addIncomingReference(JSCell*);
79
80 // A filter function returns true if we wish to keep the incoming
81 // reference, and false if we don't. This may delete the object,
82 // and if it does so, this returns true. In general, you don't want
83 // to use this with a filter function that can return false unless
84 // you're also walking the GC's list.
85 template<typename FilterFunctionType>
86 bool filterIncomingReferences(FilterFunctionType&);
87
88private:
89 static uintptr_t singletonFlag() { return 1; }
90
91 bool hasVectorOfCells() const { return !(m_encodedPointer & singletonFlag()); }
92 bool hasAnyIncoming() const { return !!m_encodedPointer; }
93 bool hasSingleton() const { return hasAnyIncoming() && !hasVectorOfCells(); }
94
95 JSCell* singleton() const
96 {
97 ASSERT(hasSingleton());
98 return bitwise_cast<JSCell*>(m_encodedPointer & ~singletonFlag());
99 }
100
101 Vector<JSCell*>* vectorOfCells() const
102 {
103 ASSERT(hasVectorOfCells());
104 return bitwise_cast<Vector<JSCell*>*>(m_encodedPointer);
105 }
106
107 // Singleton flag is set: this is a JSCell*.
108 // Singleton flag not set: this is a pointer to a vector of cells.
109 uintptr_t m_encodedPointer;
110};
111
112} // namespace JSC
113
114#endif // GCIncomingRefCounted_h
115
116